Three variants of schlieren techniques are employed to investigate the development of second-mode instability waves in the hypersonic boundary layer of a slender cone in a reflected shock tunnel. First, a previously proposed technique using high frame rate (i.e., at least as high as the dominant instability frequency) schlieren visualization with a continuous light source is shown to provide repeatable measurements of the instability propagation speed and frequency. A modified version of the technique is then introduced whereby a pulsed light source allows the use of a higher-resolution camera with a lower frame rate: this provides significant benefits in terms of spatial resolution and total recording time. A detailed picture of the surface-normal intensity distribution for individual wave packets is obtained, and the images provide comprehensive insight into the unsteady flow structures within the boundary layer. Finally, two-point schlieren deflectometry is implemented and shown to be capable of providing second-mode growth information in the challenging shock tunnel environment. © 2014 Springer-Verlag Berlin Heidelberg.
CITATION STYLE
Laurence, S. J., Wagner, A., & Hannemann, K. (2014). Schlieren-based techniques for investigating instability development and transition in a hypersonic boundary layer. Experiments in Fluids, 55(8). https://doi.org/10.1007/s00348-014-1782-9
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